Ride height on vehicles equipped with an electronically controlled suspension is monitored by a ride height sensor connected between a suspension member and the body of the vehicle. On vehicles having load leveling, air, hydropneumatic or hydraulic suspension systems, it is necessary to know the ride height of the vehicle in order to determine whether correction of the ride height is required. For example, in the event that the ride height is less than prescribed limits, as determined by the height sensor, an adjustable suspension unit may be given the command to increase the ride height. Conversely, in the event that the ride height exceeds the prescribed limits, the adjustable suspension unit may be given the command to lower or decrease the ride height.
Current manufacturing technology calls for attachment of the height sensor to the vehicle to be "trend set" or placed and adjusted on the vehicle during the assembly process using data provided from a small sample of previously built vehicles. Alternatively, a means of measuring the distance between the sensor attachment points at a known suspension position relative to the body can be used to attempt to accurately position the sensor. Both of these processes attempt to overcome the natural manufacturing build variation of the vehicle. Unfortunately, both of these processes are inherently imprecise, inaccurate, and labor intensive, leading to vehicles that lean, display improper attitude, and suffer from alignment drift and pull.
An apparatus and method for calibrating a vehicle suspension control module is disclosed in U.S. Pat. No. 5,267,466, assigned to the assignee of the present invention, and which is hereby incorporated by reference. That apparatus comprises first means, such as a laser, for measuring an actual ride height of a vehicle, second means, such as a linear height sensor, for measuring the distance between the sprung and unsprung vehicle mass, and a processor for comparing the first and second signals and for calculating a deviation therebetween which is stored in the suspension control module. The processor also adjusts the second signal by the deviation to provide correlation between the sprung and unsprung vehicle mass, and the actual ride height of the vehicle. That calibration apparatus and method, however, measures ride height with respect to ground and does not take into account several sources of error, particularly tire pressure variation, rigid body cross-talk, and suspension control system over/undershoot. Such errors can lead to inaccurate ride height determination. In addition, there is no provision in the prior apparatus for centering the vehicle relative to the first measurement means, the laser, resulting in inexact measurement.
An object of the present invention is to provide an apparatus for more accurately calibrating a suspension control module which measures ride height with respect to a vehicle coordinate system.
It is also an object of the present invention to provide an apparatus for calibrating a suspension control module which may be utilized in a factory setting in a cost and time efficient manner.
Yet another object of the present invention is to provide an apparatus for calibrating a suspension control module which corrects for vehicle rigid body cross-talk and for air suspension control system overshoot or undershoot.
It is an advantage of the present invention that vehicle ride height is measured with reference to a vehicle coordinate system and not to the surface upon which the vehicle rests.
Another advantage is that the apparatus of the present invention is capable of calibrating the suspension control module accurately regardless of tire pressure.
It is a feature of the present invention that the vehicle is centered with respect to the ride height measurement instruments prior to calibrating the suspension control module.
Another feature of the present invention is the measurement of ride height as a function of control arm angle.
It is another feature of the present invention that the apparatus for calibrating a suspension control module measures ride height with two lasers at each vehicle corner so that ride height can be accurately measured.
These and other objects, advantages, and features of the present invention will become apparent from the summary, drawings, detailed description and claims which follow.